Firewalls are typically used to control access from outside users on the Internet to networks such as local area networks or intranets. A firewall monitors traffic between the Internet and the protected network to prevent unauthorized entry by hackers or other malicious users. In lieu of a firewall, each host on the protected network would have to guard against such entry. Because only one host with a poorly-chosen password would jeopardize the entire network in such a case, a firewall provides a centralized security solution that alleviates policing by each host.
Network firewalls provide security in a number of fashions. For example, in a packet-filtering scheme, incoming and outgoing packets may be inspected so that non-conforming packets may be removed. Alternatively, a proxy server may be used to prevent any direct connections between hosts on the protected network and outside users on the Internet.
Regardless of the manner in which a firewall provides security to the protected network, situations arise in which outside users must communicate with devices or hosts within the protected network. For example, users may desire support of their networked devices by the device manufacturer. To gain electronic access to these devices, the manufacturer must cross the network firewall. For example, a port may be maintained in the firewall such as that provided for in a virtual private network (VPN) to allow outside users to penetrate the firewall. But maintaining such a port, even under the security of a VPN, allows a determined and sophisticated outsider means of accessing the protected network.
Accordingly, there is a need in the art for improved firewall penetration techniques that do not require a dedicated open port in the firewall.